This invention relates generally to bumpers and, more particularly, to bumper beams.
Bumpers typically extend widthwise across the front and rear of a vehicle and are mounted to rails that extend in a lengthwise direction. A typical bumper includes a steel beam or reinforcing member attached to vehicle rails and covered by a fascia. Such steel beams are heavy and typically deform, or buckle, on impact. Energy from an impact therefore may be transferred to the vehicle rails and result in additional damage to the vehicle.
Energy absorbing bumper systems attempt to reduce vehicle damage as a result of a collision by managing impact energy and intrusion while not exceeding a rail load limit of the vehicle. The efficiency of a bumper system is defined as the amount of energy absorbed over distance. A high efficiency bumper system absorbs more energy over a shorter distance than a low efficiency bumper system. High efficiency is achieved by building load quickly to just under the rail load limit and maintaining that load constant until the impact energy has been dissipated.
Some known energy absorbing bumper systems include a beam and an energy absorber coupled to the beam. The energy absorber is effective in absorbing energy from an impact. Separately fabricating an energy absorber and assembling the energy absorber to the beam increases both the fabrication and assembly costs of a bumper assembly as compared to a simple steel beam bumper.
Other known energy absorbing bumper systems utilize a foam resin, such as described in U.S. Pat. No. 4,762,352 and U.S. Pat. No. 4,941,701. Foam based systems typically have slow loading upon impact, which results in a high displacement. Further, foams are effective to a sixty or seventy percent compression, and beyond that point, foams become incompressible so that the impact energy is not fully absorbed. The remaining impact energy is absorbed through deformation of a backup beam and/or vehicle structure. Foams are also temperature sensitive so that displacement and impact absorption behavior can change substantially with temperature. Typically, as temperature is lowered, foam becomes more rigid, resulting in higher loads. Conversely, as temperature rises, foams become more compliant resulting in higher displacements and possible vehicle damage.
Still other known bumper systems include crash cans. The crash cans are separately fabricated and attached directly to a beam in alignment with the vehicle rails. The crash cans absorb energy during impact, e.g., an offset impact, and facilitate preventing damage to the beam. Separately fabricating and attaching the crash cans to the beam, however, increases bumper assembly costs and complexity.